This is a trivialised example highlighting my situation:
ProxyPass /google/ http://www.google.com/
ProxyPassReverse /google/ http://www.google.com/
<VirtualHost 127.0.0.1:82>
ProxyPass /google/ http://www.yahoo.com/
ProxyPassReverse /google/ http://www.yahoo.com/
</VirtualHost>
In this case a request "http://127.0.0.1:82/google/" will try to go to http://www.google.com
I have also found that a ProxyPass defined in main will take precedence over actual directories available in a vhost - eg if in above instead of the VirtualHost having ProxyPass rules its DocumentRoot contained a directory named "google" the Proxy would still be in effect.
Per the apache docs, I had been led to believe any "main" definition would be overridden by a VirtualHost able to satisfy the request.
Unfortunately, You are right. I don't know if this would be right, but you may remedy it by including the default proxy options to [VirtualHost default] section (http://httpd.apache.org/docs/2.0/vhosts/examples.html#default) like this: